Goods are often transported by a carrier having some form of platform or bunk upon which the goods are placed, such as, but not limited to, a flat bed trailer. The goods must be secured in order to prevent any moving or shifting which could damage the goods and cause unsafe driving conditions. Various tie down assemblies have been developed for the purpose of securing goods being transported on a carrier.
The tie down straps are typically fastened and tensioned with the aid of a winch having a manual ratchet mechanism. Such ratchet mechanisms are known in the art, for example, as shown in U.S. Pat. Nos. 4,045,002 and 5,853,164, and may be used for several fastening applications. The inherent limitation with these systems is the lack of monitoring and appropriate automatic adjustment of the strap tension during transit. This problem is a very common concern for flatbed trailers carrying cargo for the transportation industry. Operators are left wondering if they have adequately secured their cargo before departure and especially during transit, when the contents may shift slightly, adversely impacting on the tension of the strap and on the load distribution. Another weakness with the manual ratchet mechanism is the risk of injury to the operator. To manually secure tie downs, operators have to exert large forces, which often lead to physical injury.
An automatic take-up winch is taught in U.S. Pat. No. 4,036,476 to Douce. The Douce device employs an actuating unit that advances the winch by applying force on the teeth of the ratchet wheel, one tooth at a time. While the automatic take-up winch of the '476 patent overcomes the deficiency of the strictly manual winches, it suffers from a number of its own deficiencies. For example, because the Douce winch relies on the direct application of force against a tooth of the ratchet wheel, the force required is very high. The device therefore requires a strong source of pressure, which can be problematic given the small amount of available space below the carrier. In addition, the Douce invention is susceptible to failure as a result of debris build-up on the ratchet wheel teeth since the actuating unit needs to directly engage each tooth. The constant force being applied to the teeth also leads to increased wear of the teeth such that over time they will require replacement. Furthermore, the entire actuating unit and winch is one pre-formed unit such that the actuating unit may not be used in association with the winches that are already mounted on a carrier.
A further strap tensioning system is taught in International Publication Number WO 03/013906 filed by Brunet. The Brunet application teaches a strap winch device for automatically tightening a strap to a pre-selected tension. A number of the winch devices are fitted on a flat bed trailer and are connected to a single fore and aft drive shaft which extends along the side of the trailer. The drive shaft is driven by a motor to tighten any straps that require tightening. Each winch device has a clutch mechanism to prevent the motor from overheating once a set tightening torque threshold has been reached. The device is also equipped with a manual clutch override so that an operator can release the tension of a given winch device whenever necessary. The clutch assembly has a discoid casing having a number of deep cylindrical radial recesses. Spring loaded spheroid bodies are sized to fit into the radial recesses. The discoid casing is fitted within a ring gear powered by the drive shaft. The ring gear has shallow, arcuate recesses within which the spheroid bodies may be fitted. Power from the motor is transferred from the shaft to the ring gear and from the ring gear to the discoid casing. The discoid casing has a small gear wheel anchored to it which in turn transfers rotational force to the tensioning gear thereby tightening the strap. Once the strap has been tightened to a set torque threshold, the radial springs inside the discoid casing will yieldingly move radially inwardly thereby releasing the frictional interlock between the discoid casing and the ring gear. Once this pre-selected tension level has been achieved, while the electric motor continues to rotate the shaft and the ring gear, rotational forces are no longer transferred to the discoid casing.
The Brunet device suffers from a number of drawbacks. It requires power from an electric motor. The motor must be sufficiently powerful to operate all winches at the same time, as they are linked in series. Should the motor fail, none of the winches will work. Similarly, the system will only operate when the motor is running. In addition, the complex gear system and clutch of the Brunet device will make identifying any problems with the system difficult and ongoing maintenance costly and time consuming. The shaft driving the devices runs along the length of the side of the trailer and would be susceptible to having objects getting wrapped around it and hindering its ability to rotate. Finally, it would be difficult to retro-fit existing trailers with the Brunet system due to the complex nature of the mechanism and limited space under the trailer for attachment likely requiring the removal of any existing winches.
Accordingly, it is an object of an embodiment of the present invention to provide an automated tie down device having a torque transfer mechanism that can easily be released without the use of any strenuous effort by the operator.
It is an object of an embodiment of the invention to provide an automated tie down device powered by pneumatics without the use of electronics.
It is a further object of an embodiment of the present invention to overcome the deficiencies noted above. Other objects of the invention will be apparent from the description that follows.